The production of paper products involves the utilization of wood fiber that is extracted out of wood particles such as wood chips, e.g. chunks of wood of varying thickness in a range of about 3/8 inch to 1 inch. The wood chips are, in effect, cooked under controlled conditions resulting in the fibers being released from the structure of the wood. These fibers are suspended in a slurry that is referred to as pulp. The pulp is subsequently used as the primary ingredient for producing paper.
Many different types of paper are produced from wood pulp and the different types have different strength requirements. For example, newspaper, wrapping paper, and the like, must be stronger than tissue paper or writing paper. Tissue paper must be softer and in some applications, tear easily. Also, a paper's strength is negatively effected by bleaching which is required for some paper products (writing paper and tissue paper) while other paper products remain unbleached (cardboard boxes and grocery bags). It is the length of the wood fibers of the pulp that largely determines the strength of the paper.
As a control factor for determining the makeup of the fibers that go into the pulp mixture for making the various paper products, the pulp mixture is graded according to burst strength, tear strength and breaking strength. These strength characteristics are collectively referred to as the pulp's TSF (total strength factor). A high TSF requirement generally demands a greater proportion of long fibered pulp.
Paper products such as tissue paper, are commonly produced from pulp that has a low TSF. Such pulp can be produced from short wood fibers or it can be produced from a combination of the larger fibers of chip pulp and limited amounts of sawdust pulp. Sawdust pulp is generally considered merely a filler material, i.e. without significant TSF. In mills that use sawdust pulp, up to about 20% of the pulp mixture used for tissue paper production may be filler or sawdust pulp. The main reason that sawdust is used at all is that there are enormous quantities of sawdust available from lumber production and sawdust costs less than half the cost of wood chips.
Historically, sawdust was used in paper production to a greater proportion than exists currently. The reason is that sawmills have become more efficient in utilizing the log. Early saws created wide kerfs and in the process removed large sawdust particles (although small as compared to wood chip size). In tissue paper production the large sawdust particles were used at about a 70/30 ratio (chip pulp to sawdust pulp). As sawdust particles decreased in size, that ratio changed to about an 80/20 ratio which is commonly in use today. The reduction in size of the sawdust particles in producing sawdust pulp resulted in higher cost for tissue paper production as more and more of the higher priced wood chips were required.